1. Field of the Invention
This application relates generally to the deposition of silicon-containing materials in semiconductor processing. More particularly, this application relates to the selective deposition of epitaxial, silicon-containing films using BCl3 and a silicon source.
2. Description of the Related Art
It is often desirable to selectively deposit silicon or silicon germanium on semiconductor surfaces without depositing on insulating surfaces. For example, heterojunction bipolar transistors are often fabricated using selective deposition techniques that deposit epitaxially, e.g., single-crystal, semiconductor films only on active areas. Other transistor designs benefit from elevated source/drain structures, which provide additional silicon that can be consumed by the source/drain contact process without altering shallow junction device performance. Selective epitaxy advantageously reduces the need for subsequent patterning and etch steps.
While selective deposition processes are known in the art, continued scaling in pursuit of faster, less power-hungry circuitry has increased the demands on integrated circuit fabrication. Generally speaking, selectivity takes advantage of differential nucleation during deposition on disparate materials. Selective deposition can generally be explained by simultaneous etching and deposition of the material being deposited. The precursor of choice will generally have a tendency to nucleate and grow more rapidly on one surface and less rapidly on another surface. For example, silane will generally nucleate on both silicon oxide and silicon, but there is a longer nucleation phase on silicon oxide. At the beginning of a nucleation stage, discontinuous films on oxide have a high exposed surface area relative to merged, continuous films on silicon. Accordingly, an etchant, such as HCl, added to the process will have a greater effect upon the poorly nucleating film on the oxide as compared to the rapidly nucleating film on the silicon. The relative selectivity of a process can thus be tuned by adjusting factors that affect the deposition rate, such as precursor flow rates, temperature, pressure, and the rate of etching, such as etchant flow rate, temperature, and/or pressure. Changes in each variable will generally have different effects upon etch rate and deposition rate. Typically, a selective deposition process is tuned to produce the highest deposition rate feasible on the window of interest while accomplishing no deposition in the field regions. Known selective silicon deposition processes include reactants silane and hydrochloric acid with a hydrogen carrier gas.
While many selective deposition techniques are known, there is a need for deposition processes with improved methods of selective semiconductor deposition, along with improved uniformity, purity, deposition speed and repeatability.